/*
 * Copyright (C) 2008 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import java.util.Map;

import javax.annotation.Nullable;

import com.google.common.annotations.GwtCompatible;

/**
 * Implementation of {@link ImmutableMap} with exactly one entry.
 * 
 * @author Jesse Wilson
 * @author Kevin Bourrillion
 */
@GwtCompatible(serializable = true)
@SuppressWarnings("serial")
// uses writeReplace(), not default serialization
final class SingletonImmutableMap<K, V> extends ImmutableMap<K, V> {
    final transient K singleKey;
    final transient V singleValue;

    private transient Entry<K, V> entry;

    SingletonImmutableMap(K singleKey, V singleValue) {
        this.singleKey = singleKey;
        this.singleValue = singleValue;
    }

    SingletonImmutableMap(Entry<K, V> entry) {
        this.entry = checkNotNull(entry); // checkNotNull for GWT.
        this.singleKey = checkNotNull(entry.getKey()); // checkNotNull for GWT.
        this.singleValue = checkNotNull(entry.getValue()); // checkNotNull for
                                                           // GWT.
    }

    private Entry<K, V> entry() {
        Entry<K, V> e = entry;
        return (e == null) ? (entry = Maps.immutableEntry(singleKey,
                singleValue)) : e;
    }

    @Override
    public V get(Object key) {
        return singleKey.equals(key) ? singleValue : null;
    }

    public int size() {
        return 1;
    }

    @Override
    public boolean isEmpty() {
        return false;
    }

    @Override
    public boolean containsKey(Object key) {
        return singleKey.equals(key);
    }

    @Override
    public boolean containsValue(Object value) {
        return singleValue.equals(value);
    }

    private transient ImmutableSet<Entry<K, V>> entrySet;

    @Override
    public ImmutableSet<Entry<K, V>> entrySet() {
        ImmutableSet<Entry<K, V>> es = entrySet;
        return (es == null) ? (entrySet = ImmutableSet.of(entry())) : es;
    }

    private transient ImmutableSet<K> keySet;

    @Override
    public ImmutableSet<K> keySet() {
        ImmutableSet<K> ks = keySet;
        return (ks == null) ? (keySet = ImmutableSet.of(singleKey)) : ks;
    }

    private transient ImmutableCollection<V> values;

    @Override
    public ImmutableCollection<V> values() {
        ImmutableCollection<V> v = values;
        return (v == null) ? (values = new Values<V>(singleValue)) : v;
    }

    // uses writeReplace(), not default serialization
    private static class Values<V> extends ImmutableCollection<V> {
        final V singleValue;

        Values(V singleValue) {
            this.singleValue = singleValue;
        }

        @Override
        public boolean contains(Object object) {
            return singleValue.equals(object);
        }

        @Override
        public boolean isEmpty() {
            return false;
        }

        public int size() {
            return 1;
        }

        @Override
        public UnmodifiableIterator<V> iterator() {
            return Iterators.singletonIterator(singleValue);
        }
    }

    @Override
    public boolean equals(@Nullable Object object) {
        if (object == this) {
            return true;
        }
        if (object instanceof Map) {
            Map<?, ?> that = (Map<?, ?>) object;
            if (that.size() != 1) {
                return false;
            }
            Entry<?, ?> entry = that.entrySet().iterator().next();
            return singleKey.equals(entry.getKey())
                    && singleValue.equals(entry.getValue());
        }
        return false;
    }

    @Override
    public int hashCode() {
        return singleKey.hashCode() ^ singleValue.hashCode();
    }

    @Override
    public String toString() {
        return new StringBuilder().append('{').append(singleKey.toString())
                .append('=').append(singleValue.toString()).append('}')
                .toString();
    }
}
